FIG. 14 is a block diagram showing a configuration of a conventional signal transmission system disclosed in the following Non-Patent Document 1.
The signal transmission system shown in FIG. 14 comprises a pulse width modulator 101 and a transmission frequency converter 102 in a transmission side.
In addition, it comprises a receiving frequency converter 103 and a decoder 104 in a receiving side via a transmission line, and the decoder 104 comprises a data detector 105 and a delay circuit 106 (the amount of delay T=0.5 T).
Next, the operation will be described.
In the transmission side, the pulse width modulator 101 is supplied with transmission data (“0” or “1”) with a period T, generates a modulation signal (PWM signal) with a pulse width corresponding to the transmission data, and the transmission frequency converter 102 converts it to a desired carrier frequency and transmits it.
It is assumed here that the transmission data “0” has a pulse width not greater than 0.5 T (0.25 T, for example), and the transmission data “1” has a pulse width not less than 0.5 T (0.75 T, for example).
In the receiving side, the receiving frequency converter 103 carries out the frequency conversion of the PWM signal to a baseband, and supplies it to the decoder 104.
In the decoder 104, using as the clock the PWM signal to which a 0.5 T time delay is added through the delay circuit 106, the data detector 105 operates in synchronization with a rising edge of the clock, and samples the PWM signal to obtain the received data.
FIG. 15 shows an example of the temporal waveforms of the transmission data, PWM signal, clock, and received data.
As described above, by using the received PWM signal as the clock, the conventional signal transmission system can obtain the received data without using such a clock generator as disclosed in the following Patent Document 1.